soc: qcom/spm: shut up uninitialized variable warning

gcc warns about the 'found' variable possibly being used uninitialized:

drivers/soc/qcom/spm.c: In function 'spm_dev_probe':
drivers/soc/qcom/spm.c:305:5: error: 'found' may be used uninitialized in this function [-Werror=maybe-uninitialized]

However, the code is correct because we know that there is
always at least one online CPU. This initializes the 'found'
variable to zero before the loop so the compiler knows
it does not have to warn about it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>