flashrom.c, sfdp.c: Initialize dynamically allocated memory using calloc

In flashrom_image_write variables curcontents and oldcontents are
dynamically allocated using malloc. These could remain uninitialized and
when later used in need_erase could result in undefined behaviour.
Similiar reasoning for variables hbuf, hdrs, tbuf in function
prob_spi_sfdp. So allocate them using calloc to initialize them to
zeroes or if allocating using malloc separately initialize them using a loop.

Change-Id: I6b9269129968fb3b55b0d2a2e384c8a1aeba43ab
Signed-off-by: Aarya Chaumal <aarya.chaumal@gmail.com>
---
M flashrom.c
M sfdp.c
M writeprotect_ranges.c
3 files changed, 5 insertions(+), 8 deletions(-)