spi: mxc_spi: fix warnings if CLK_ENABLED not set

Following warnings (unused variables) are raised:

drivers/spi/mxc_spi.c: In function 'mxc_spi_probe':
drivers/spi/mxc_spi.c:595:14: error: unused variable 'blob' [-Werror=unused-variable]
595 |  const void *blob = gd->fdt_blob;
    |              ^~~~
drivers/spi/mxc_spi.c:594:6: error: unused variable 'node' [-Werror=unused-variable]
594 |  int node = dev_of_offset(bus);

Move the variable declaration inside the code where they are used.

Signed-off-by: Stefano Babic <sbabic@denx.de>