Linux 6.1 compat: change order of sys/mutex.h includes

After Linux 6.1-rc1 came out, the build started failing to build a
couple of the files in the linux spl code due to the mutex_init
redefinition. Moving the sys/mutex.h include to a lower position within
these two files appears to fix the problem.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #14040