cxgb4: fix missing break in switch and indent return statements

The break statement for the Macronix case is missing and will
fall through to the Winbond case and re-assign the size setting.
Fix this by adding the missing break statement.  Also correctly
indent the return statements.

Detected by CoverityScan, CID#1458020 ("Missing break in switch")

Fixes: 96ac18f1 ("cxgb4: Add support for new flash parts")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>