locking/mutex: Define mutex_init() once

locking/mutex: Define mutex_init() once

With CONFIG_PREEMPT_RT disabled __mutex_init() is a function. With
CONFIG_PREEMPT_RT enabled, __mutex_init() is a macro. I assume this is why
mutex_init() is defined twice as exactly the same macro.

Prepare for introducing a new macro for mutex initialization by combining
the two identical mutex_init() definitions into a single definition. This
patch does not change any functionality because the C preprocessor expands
macros when it encounters the macro name and not when a macro definition
is encountered. See also commit bb630f9f7a7d ("locking/rtmutex: Add mutex
variant for RT").

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240912223956.3554086-2-bvanassche@acm.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>