mtd: spi-nor: slightly change code style in spi_nor_sr_ready()

Now that there is almost no special case code left in
spi_nor_sr_ready(), the return check looks odd. Move the function call
closer to the return code checking.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20220223134358.1914798-32-michael@walle.cc