hwmon: (macsmc) Fix overflows, underflows, and sign extension

hwmon: (macsmc) Fix overflows, underflows, and sign extension

The macsmc-hwmon driver experienced several issues related to value
scaling and type conversion:

1. macsmc_hwmon_read_f32_scaled() clipped values to INT_MAX/INT_MIN.
   On 64-bit systems, hwmon supports long values, so clipping to
   32-bit range was premature and caused loss of range for high-power
   sensors. Changed it to use long and clip to LONG_MAX/LONG_MIN.
2. The overflow check in macsmc_hwmon_read_f32_scaled() used 1UL,
   which is 32-bit on some platforms. Switched to 1ULL.
3. macsmc_hwmon_read_key() used a u32 temporary variable for f32
   values. When assigned to a 64-bit long, negative values were
   zero-extended instead of sign-extended, resulting in large
   positive numbers.
4. macsmc_hwmon_read_ioft_scaled() used mult_frac() which could
   overflow during intermediate multiplication. Switched to
   mul_u64_u32_div() to handle the 64-bit multiplication safely.
5. ioft values (unsigned 48.16) could overflow long when scaled
   by 1,000,000. Added explicit clipping to LONG_MAX in the caller.
6. macsmc_hwmon_write_f32() truncated its long argument to int,
   potentially causing issues for large values.

Fix these issues by using appropriate types and helper functions.

Fixes: 785205fd8139 ("hwmon: Add Apple Silicon SMC hwmon driver")
Cc: James Calligeros <jcalligeros99@gmail.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Neal Gompa <neal@gompa.dev>
Cc: Janne Grunau <j@jannau.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20260129175112.3751907-3-linux@roeck-us.net
Reviewed-by: James Calligeros <jcalligeros99@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>