spi: zynqmp_qspi: Mark zynqmp_qspi_set_tapdelay() as static

Fix the following sparse and compile time warning triggered with W=1:

drivers/spi/zynqmp_gqspi.c:286:6:
warning: no previous prototype for 'zynqmp_qspi_set_tapdelay'
[-Wmissing-prototypes]

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://lore.kernel.org/r/20221004053730.25602-1-venkatesh.abbarapu@amd.com


Signed-off-by: Michal Simek <michal.simek@amd.com>