board: ti: am62ax: env: Use default MMC related args

board: ti: am62ax: env: Use default MMC related args

There are common MMC args for TI plats in include/environment/ti/mmc.env.
Since we already include this, there is no need to redefine these
MMC vars. Use the defaults.

This seems like something that could have been done while refactoring
these vars in the first place as it happened after this AM62A file
was available hence the fixes tag.

Reported-by: Chirag Shilwant <c-shilwant@ti.com>
Fixes: 3709b529156e ("env: ti: mmc.env: Move mmc related args to common place")
Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Acked-by: Chirag Shilwant <c-shilwant@ti.com>
Reviewed-by: Judith Mendez <jm@ti.com>