serial: imx: TX DMA: clean up sg initialization
serial: imx: TX DMA: clean up sg initialization

Inverting the logic of the if statement for the sg initialization
makes the if statement easier and better to read.

No functional change.

Signed-off-by: Dirk Behme <65191830245723325aed938dddb6d81810e13fc4@de.bosch.com>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs