spi: tegra20-sflash: fix to check return value of platform_get_irq() in tegra_sflash_probe()

The platform_get_irq might be failed and return a negative result. So
there should have an error handling code.

Fixed this by adding an error handling code.

Fixes: 8528547b

 ("spi: tegra: add spi driver for sflash controller")
Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
Link: https://lore.kernel.org/r/tencent_71FC162D589E4788C2152AAC84CD8D5C6D06@qq.com


Signed-off-by: Mark Brown <broonie@kernel.org>