mfd: si476x: Fix kernel-doc warnings

mfd: si476x: Fix kernel-doc warnings

Add kernel-doc entries for missing fields or correct some typos
in names to eliminate kernel-doc warnings:

Warning: include/linux/mfd/si476x-core.h:156 struct member 'regmap' not
 described in 'si476x_core'
Warning: include/linux/mfd/si476x-core.h:156 struct member 'power_state'
 not described in 'si476x_core'
Warning: include/linux/mfd/si476x-core.h:156 struct member 'supplies' not
 described in 'si476x_core'
Warning: include/linux/mfd/si476x-core.h:156 struct member 'is_alive' not
 described in 'si476x_core'
Warning: include/linux/mfd/si476x-core.h:156 struct member 'rds_fifo_depth'
 not described in 'si476x_core'
Warning: include/linux/mfd/si476x-core.h:170 function parameter 'core' not
 described in 'si476x_core_lock'
Warning: include/linux/mfd/si476x-core.h:179 function parameter 'core' not
 described in 'si476x_core_unlock'
Warning: include/linux/mfd/si476x-core.h:259 struct member 'firmware' not
 described in 'si476x_func_info'
Warning: include/linux/mfd/si476x-core.h:335 struct member 'rds' not
 described in 'si476x_rds_status_report'

I don't know what the 'ble' field is so I didn't add a kernel-doc comment
for it:
  Warning: include/linux/mfd/si476x-core.h:335 struct member 'ble' not
    described in 'si476x_rds_status_report'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20260309214223.749088-5-rdunlap@infradead.org
Signed-off-by: Lee Jones <lee@kernel.org>