spi: spi-mpc52xx-psc: Fix an unsigned comparison that can never be negative

spi: spi-mpc52xx-psc: Fix an unsigned comparison that can never be negative

In struct mpc52xx_psc_spi, the variable 'irq' is declared as an unsigned int.
The comparison of variable 'irq'  with signed int operand is incorrect. Also,
the return value from the call to platform_get_irq(pdev,0) is int and it is
assigned to an unsigned int variable 'irq', thus redeclaring the type of
variable 'irq' to signed int.

This fixes warning such as:
drivers/spi/spi-mpc52xx-psc.c:332:5-13:
WARNING: Unsigned expression compared with zero: mps -> irq < 0

Signed-off-by: Rajeshwar R Shinde <coolrrsh@gmail.com>
Link: https://lore.kernel.org/r/20230807144942.30317-2-coolrrsh@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>