spi: xilinx_spi: Modify transfer logic xilinx_spi_xfer() function

[u-boot] / board / sr1500 / MAINTAINERS

SOCFPGA SR1500 BOARD
M:      Stefan Roese <sr@denx.de>
S:      Maintained
F:      board/sr1500/
F:      include/configs/socfpga_sr1500.h
F:      configs/socfpga_sr1500_defconfig