scsi: ufs: fixing the change power function

In the "ufshcd_config_max_pwr_mode" function, we assume power
change only occurs into HS mode (FAST_MODE or FASTAUTO_MODE).
this is a wrong assumption, as the specific preferences of the
vendor can be set to PWM (SLOW_MODE or SLOWAUTO_MODE) as well.

Change-Id: I4dc860a25a9477879766632359de9e534db309f2
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>