tools/mrvl_uart.sh: Tidy script output

tools/mrvl_uart.sh: Tidy script output

Fix a typo in help output (awailable -> available).
Tidy the grammar - not the board connects to a port, we do.

While at it, be consistent in upper-casing the comments.

Fixes: eee4835d22 ("tools: Add Marvell recovery image download script")
Cc: Konstantin Porotchkin <[email protected]>
Cc: Stefan Roese <[email protected]>
Cc: Igal Liberman <[email protected]>
Signed-off-by: Andreas Färber <[email protected]>
Reviewed-by: Konstantin Porotchkin <[email protected]>
Reviewed-by: Stefan Roese <[email protected]>
Signed-off-by: Stefan Roese <[email protected]>