counter: rz-mtu3-cnt: prevent counter from being toggled multiple times

counter: rz-mtu3-cnt: prevent counter from being toggled multiple times

Runtime PM counter is incremented / decremented each time the sysfs
enable file is written to.

If user writes 0 to the sysfs enable file multiple times, runtime PM
usage count underflows, generating the following message.

rz-mtu3-counter rz-mtu3-counter.0: Runtime PM usage count underflow!

At the same time, hardware registers end up being accessed with clocks
off in rz_mtu3_terminate_counter() to disable an already disabled
channel.

If user writes 1 to the sysfs enable file multiple times, runtime PM
usage count will be incremented each time, requiring the same number of
0 writes to get it back to 0.

If user writes 0 to the sysfs enable file while PWM is in progress, PWM
is stopped without counter being the owner of the underlying MTU3
channel.

Check against the cached count_is_enabled value and exit if the user
is trying to set the same enable value.

Cc: stable@vger.kernel.org
Fixes: 0be8907359df ("counter: Add Renesas RZ/G2L MTU3a counter driver")
Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Link: https://lore.kernel.org/r/20260130122353.2263273-5-cosmin-gabriel.tanislav.xa@renesas.com
Signed-off-by: William Breathitt Gray <wbg@kernel.org>