scsi: ufs: core: Rename ufshcd_wb_presrv_usrspc_keep_vcc_on()

scsi: ufs: core: Rename ufshcd_wb_presrv_usrspc_keep_vcc_on()

The ufshcd_wb_presrv_usrspc_keep_vcc_on() function has deviated from its
original implementation. The "_keep_vcc_on" part of the function name is
misleading. Rename the function to ufshcd_wb_curr_buff_threshold_check()
to improve the readability. Also, updated the comments in the function.
There is no change to the functionality.

Signed-off-by: Bao D. Nguyen <quic_nguyenb@quicinc.com>
Link: https://lore.kernel.org/r/02ae5e133f6ebf23b54d943e6d1d9de2544eb80e.1743192926.git.quic_nguyenb@quicinc.com
Reviewed-by: Avri Altman <avri.altman@sandisk.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>