net/e1000/base: fix build with gcc 6

net/e1000/base: fix build with gcc 6

Add the missing braces to the 'if' statements to fix the misleading
identation. This also fixes the following build errors when building
with gcc >= 6:

drivers/net/e1000/base/e1000_phy.c:4156:2:
error: this 'if' clause does not guard... [-Werror=misleading-indentation]
    if (locked)

drivers/net/e1000/base/e1000_phy.c:4158:3:
note: ...this statement, but the latter is misleadingly indented as if
it is guarded by the 'if'
    if (!ready)

drivers/net/e1000/base/e1000_phy.c:4221:2:
error: this 'if' clause does not guard... [-Werror=misleading-indentation]
    if (locked)

drivers/net/e1000/base/e1000_phy.c:4223:3:
note: ...this statement, but the latter is misleadingly indented as if
it is guarded by the 'if'
    if (!ready)

Signed-off-by: Markos Chandras <mchandras@suse.de>