Apply only valid chip select value. This change fixes case where chip
select is set to initial value of '-1' during probe and PM supend and
subsequent resume can try to use the value with undefined behaviour.
Also in case where gpio based chip select, the check in
bcm_qspi_chip_select() shall prevent undefined behaviour on resume.
Fixes: fa236a7ef240 ("spi: bcm-qspi: Add Broadcom MSPI driver")
Signed-off-by: Kamal Dasu <kdasu.kdev@xxxxxxxxx>